If you will camp in areas that only provide 30 amp service, you'll also need a dogbone for 50 -30. You'll also want a surge protector. They're pricy but most of us use them and mine has saved me several times. Progressive is the most used but there are others.
On water hoses, I'd recommend getting 2 25' hoses. In most areas, one will be enough, BUT we've had several long runs in the last year where I needed my 2nd hose. I'd also get a water pressure reducer - 1 to 55psi should be fine. You'll want to use it every time. I keep it attached to my main hose. Also a "y" water adapter will come in handy to allow you to connect a 2nd hose to wash your rig, attach to the sewer flush valve, etc.
Sorry for the length.
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